This course aims to help researchers join the exciting and quickly emerging field of biomedical QPI. Quantifying cell-induced shifts in the optical path-lengths permits nanometer scale measurements of structures and motions in a non-contact, non-invasive manner. We will explain the basic principles and applications of QPI. In the first part of the course – Methods - we will cover the main approaches to QPI, including phase-shifting, off-axis, common-path, and white-light methods, together with their figures of merit. A practical guide to designing and implementing instrumentation for QPI, along with image processing techniques will be presented. The second part of the course – Applications – will review recent advances in biomedical applications of QPI. We will cover basic applications published in the recent literature on cell structure, dynamics and light scattering, as well as clinical applications such as blood testing and tissue diagnosis.